Microcurrent Stimulation Triggers MAPK Signaling and TGF-ß1 Release in Fibroblast and Osteoblast-Like Cell Lines.

Wound healing constitutes an essential process for all organisms and involves a sequence of three phases. The disruption or elongation of any of these phases can lead to a chronic or non-healing wound. Electrical stimulation accelerates wound healing by mimicking the current that is generated in the skin after any injury. Here, we sought to identify the molecular mechanisms involved in the healing process following in vitro microcurrent stimulation-a type of electrotherapy. Our results concluded that microcurrents promote cell proliferation and migration in an ERK 1/2- or p38-dependent way. Furthermore, microcurrents induce the secretion of transforming growth factor-beta-1 (TGF-ß1) in fibroblasts and osteoblast-like cells. Interestingly, transcriptomic analysis uncovered that microcurrents enhance the transcriptional activation of genes implicated in Hedgehog, TGF-ß1 and MAPK signaling pathways. Overall, our results demonstrate that microcurrents may enhance wound closure through a combination of signal transductions, via MAPK's phosphorylation, and the transcriptional activation of specific genes involved in the healing process. These mechanisms should be further examined in vivo, in order to verify the beneficial effects of microcurrents in wound or fracture healing.

Regulation and role of endogenously produced hydrogen sulfide in angiogenesis.

Recent studies have implicated endogenously produced H2S in the angiogenic process. On one hand, pharmacological inhibition and silencing of the enzymes involved in H2S synthesis attenuate the angiogenic properties of endothelial cells, including proliferation, migration and tube-like structure network formation. On the other hand, enhanced production of H2S by substrate supplementation or over-expression of H2S-producing enzymes leads to enhanced angiogenic responses in cultured endothelial cells. Importantly, H2S up-regulates expression of the key angiogenic factor vascular endothelial growth factor (VEGF) and contributes to the angiogenic signaling in response to VEGF. The signaling pathways mediating H2S-induced angiogenesis include mitogen-activated protein kinases, phosphoinositide-3 kinase, nitric oxide/cGMP-regulated cascades and ATP-sensitive potassium channels. Endogenously produced H2S has also been shown to facilitate neovascularization in prototypical model systems in vivo, and to contribute to wound healing, post-ischemic angiogenesis in the heart and other tissues, as well as in tumor angiogenesis. Targeting of H2S synthesizing enzymes might offer novel therapeutic opportunities for angiogenesis-related diseases.

ATP-sensitive potassium channel activation induces angiogenesis in vitro and in vivo.

Intense research is conducted to identify new molecular mechanisms of angiogenesis. Previous studies have shown that the angiogenic effects of hydrogen sulfide (H2S) depend on the activation of ATP-sensitive potassium channels (KATP) and that C-type natriuretic peptide (CNP), which can act through KATP, promotes endothelial cell growth. We therefore investigated whether direct KATP activation induces angiogenic responses and whether it is required for the endothelial responses to CNP or vascular endothelial growth factor (VEGF). Chick chorioallantoic membrane (CAM) angiogenesis was similarly enhanced by the direct KATP channel activator 2-nicotinamidoethyl acetate (SG-209) and by CNP or VEGF. The KATP inhibitors glibenclamide and 5-hydroxydecanoate (5-HD) reduced basal and abolished CNP-induced CAM angiogenesis. In vitro, the direct KATP openers nicorandil and SG-209 and the polypeptides VEGF and CNP increased proliferation and migration in bEnd.3 mouse endothelial cells. In addition, VEGF and CNP induced cord-like formation on Matrigel by human umbilical vein endothelial cells (HUVECs). All these in vitro endothelial responses were effectively abrogated by glibenclamide or 5-HD. In HUVECs, a small-interfering RNA-mediated decrease in the expression of the inwardly rectifying potassium channel (Kir) 6.1 subunit impaired cell migration and network morphogenesis in response to either SG-209 or CNP. We conclude that 1) direct pharmacologic activation of KATP induces angiogenic effects in vitro and in vivo, 2) angiogenic responses to CNP and VEGF depend on KATP activation and require the expression of the Kir6.1 KATP subunit, and 3) KATP activation may underpin angiogenesis to a variety of vasoactive stimuli, including H2S, VEGF, and CNP.

Hydrogen sulfide is an endogenous inhibitor of phosphodiesterase activity.

OBJECTIVE: Recent studies have demonstrated that hydrogen sulfide (H(2)S) is produced within the vessel wall from L-cysteine regulating several aspects of vascular homeostasis. H(2)S generated from cystathione γ-lyase (CSE) contributes to vascular tone; however, the molecular mechanisms underlying the vasorelaxing effects of H(2)S are still under investigation. METHODS AND RESULTS: Using isolated aortic rings, we observed that addition of L-cysteine led to a concentration-dependent relaxation that was prevented by the CSE inhibitors DL-propargylglyicine (PAG) and ß-cyano-l-alanine (BCA). Moreover, incubation with PAG or BCA resulted in a rightward shift in sodium nitroprusside-and isoproterenol-induced relaxation. Aortic tissues exposed to PAG or BCA contained lower levels of cGMP, exposure of cells to exogenous H(2)S or overexpression of CSE raised cGMP concentration. RNA silencing of CSE expression reduced intracellular cGMP levels confirming a positive role for endogenous H(2)S on cGMP accumulation. The ability of H(2)S to enhance cGMP levels was greatly reduced by the nonselective phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. Finally, addition of H(2)S to a cell-free system inhibited both cGMP and cAMP breakdown. CONCLUSIONS: These findings provide direct evidence that H(2)S acts as an endogenous inhibitor of phosphodiesterase activity and reinforce the notion that this gasotransmitter could be therapeutically exploited.

Nitric oxide stimulates interleukin-6 production in skeletal myotubes.

Strenuous exercise leads to the up-regulation of interleukin-6 (IL-6) production and enhanced nitric oxide (NO) release within the contracting skeletal muscles. In this study, we investigated whether NO regulates IL-6 production in C2C12 myotubes. These cells exhibited a concentration-dependent increase in IL-6 production upon stimulation with NO donors (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NONOate), (Z)-1-[N-(3-aminopropyl)-N-(n-propyl)amino]diazen-1-ium-1,2-diolate (PAPA-NONOate), and sodium nitroprusside (SNP). This treatment did not alter cGMP levels nor did the soluble guanylyl cyclase (sGC) inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one(ODQ), alter this response. The NO-independent sGC activator 5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine (BAY41-2272) and cyclic guanosine monophosphate (cGMP) analog 8Br-cGMP failed to induce IL-6 production. Upon exposure to NO donors, we observed an increase in Erk1/2 and p38 MAPK phosphorylation but not in SAPK/JNK. In addition, NO-induced IL-6 release was inhibited in a concentration-dependent fashion by the MEK1/2 inhibitor PD98059 and the p38 MAPK inhibitor SB203580 but not by the SAPK/JNK inhibitor SP600125. We conclude that NO-stimulated IL-6 production in differentiated C2C12 myotubes is cGMP-independent and mediated by activation of MAPK pathways.

Synthesis and biological evaluation of oxadiazole derivatives as inhibitors of soluble guanylyl cyclase.

Soluble guanylyl cyclase (sGC) is an ubiquitously expressed enzyme that generates the second messenger cGMP and hence, leads to a number of physiological responses including vasodilation, inhibition of platelet aggregation and neurotransmission. Whilst many activating and stimulating modulators of sGC were identified and studied in recent years, only two selective inhibitors are known: ODQ and NS 2028. Furthermore, a synthetic approach to these inhibitors has not been reported yet. Herein, we describe a novel and efficient synthesis of these inhibitors, as well as the preparation of three different classes of NS 2028 analogues. Biological evaluation of this library using rat aortic smooth muscle cells revealed four new compounds with good to moderate sGC inhibitory activity. Our experiments underline the major importance of the oxadiazole ring in ODQ and NS 2028 for the efficiency of this class of inhibitors.

The soluble guanylyl cyclase inhibitor NS-2028 reduces vascular endothelial growth factor-induced angiogenesis and permeability.

Nitric oxide (NO) is known to promote vascular endothelial growth factor (VEGF)-stimulated permeability and angiogenesis. However, effector molecules that operate downstream of NO in this pathway remain poorly characterized. Herein, we determined the effect of soluble guanylyl cyclase (sGC) inhibition on VEGF responses in vitro and in vivo. Treatment of endothelial cells (EC) with VEGF stimulated eNOS phosphorylation and cGMP accumulation; pretreatment with the sGC inhibitor 4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one (NS-2028) blunted cGMP levels without affecting VEGF-receptor phosphorylation. Incubation of cells with NS-2028 blocked the mitogenic effects of VEGF. In addition, cells in which sGC was inhibited exhibited no migration and sprouting in response to VEGF. To study the mechanisms through which NS-2028 inhibits EC migration, we determined the effects of alterations in cGMP levels on p38 MAPK. Initially, we observed that inhibition of sGC attenuated VEGF-stimulated activation of p38. In contrast, the addition of 8-Br-cGMP to EC stimulated p38 phosphorylation. The addition of cGMP elevating agents (BAY 41-2272, DETA NO and YC-1) enhanced EC migration. To test whether sGC also mediated the angiogenic effects of VEGF in vivo, we used the rabbit cornea assay. Animals receiving NS-2028 orally displayed a reduced angiogenic response to VEGF. As increased vascular permeability occurs prior to new blood vessel formation, we determined the effect of NS-2028 in vascular leakage. Using a modified Miles assay, we observed that NS-2028 attenuated VEGF-induced permeability. Overall, we provide evidence that sGC mediates the angiogenic and permeability-promoting activities of VEGF, indicating the significance of sGC as a downstream effector of VEGF-triggered responses.

Hydrogen sulfide is an endogenous stimulator of angiogenesis.

The goal of the current study was to investigate the role of exogenous and endogenous hydrogen sulfide (H(2)S) on neovascularization and wound healing in vitro and in vivo. Incubation of endothelial cells (ECs) with H(2)S enhanced their angiogenic potential, evidenced by accelerated cell growth, migration, and capillary morphogenesis on Matrigel. Treatment of chicken chorioallantoic membranes (CAMS) with H(2)S increased vascular length. Exposure of ECs to H(2)S resulted in increased phosphorylation of Akt, ERK, and p38. The K(ATP) channel blocker glibenclamide or the p38 inhibitor SB203580 abolished H(2)S-induced EC motility. Since glibenclamide inhibited H(2)S-triggered p38 phosphorylation, we propose that K(ATP) channels lay upstream of p38 in this process. When CAMs were treated with H(2)S biosynthesis inhibitors dl-propylargylglycine or beta-cyano-L-alanine, a reduction in vessel length and branching was observed, indicating that H(2)S serves as an endogenous stimulator of the angiogenic response. Stimulation of ECs with vascular endothelial growth factor (VEGF) increased H(2)S release, while pharmacological inhibition of H(2)S production or K(ATP) channels or silencing of cystathionine gamma-lyase (CSE) attenuated VEGF signaling and migration of ECs. These results implicate endothelial H(2)S synthesis in the pro-angiogenic action of VEGF. Aortic rings isolated from CSE knockout mice exhibited markedly reduced microvessel formation in response to VEGF when compared to wild-type littermates. Finally, in vivo, topical administration of H(2)S enhanced wound healing in a rat model, while wound healing was delayed in CSE(-/-) mice. We conclude that endogenous and exogenous H(2)S stimulates EC-related angiogenic properties through a K(ATP) channel/MAPK pathway.

Soluble guanylyl cyclase activation by HMR-1766 (ataciguat) in cells exposed to oxidative stress.

Many vascular diseases are characterized by increased levels of ROS that destroy the biological activity of nitric oxide and limit cGMP formation. In the present study, we investigated the cGMP-forming ability of HMR-1766 in cells exposed to oxidative stress. Pretreatment of smooth muscle cells with H(2)O(2) reduced cGMP production stimulated by sodium nitroprusside (SNP) or BAY 41-2272. However, pretreatment with H(2)O(2) significantly increased HMR-1766 responses. Similar results were obtained with SIN-1, menadione, and rotenone. In addition, HMR-1766 was more effective in stimulating heme-free sGC compared with the wild-type enzyme. Interestingly, in cells expressing heme-free sGC, H(2)O(2) inhibited instead of potentiated HMR-1766 responses, suggesting that the ROS-induced enhancement of cGMP formation was heme dependent. Moreover, using truncated forms of sGC, we observed that the NH(2)-terminus of the beta(1)-subunit is required for the action of HMR-1766. Finally, to study tolerance development to HMR-1766, cells were pretreated with this sGC activator and reexposed to HMR-1766 or SNP. Results from these experiments demonstrated lack of tolerance development to HMR-1766 as well as lack of cross-tolerance with SNP. We conclude that HMR-1766 is an improved sGC activator as it has the ability to activate oxidized/heme-free sGC and is resistant to the development of tolerance; these observations make HMR-1766 a promising agent for treating diseases associated with increased vascular tone combined with enhanced ROS production.

Protein kinase G phosphorylates soluble guanylyl cyclase on serine 64 and inhibits its activity.

OBJECTIVE: Binding of nitric oxide (NO) to soluble guanylyl cyclase (sGC) leads to increased cGMP synthesis that activates cGMP-dependent protein kinase (PKG). Herein, we tested whether sGC activity is regulated by PKG. METHODS AND RESULTS: Overexpression of a constitutively active form of PKG (DeltaPKG) stimulated (32)P incorporation into the alpha1 subunit. Serine to alanine mutation of putative sites revealed that Ser64 is the main phosphorylation site for PKG. Using a phospho-specific antibody we observed that endogenous sGC phosphorylation on Ser 64 increases in cells and tissues exposed to NO, in a PKG-inhibitable manner. Wild-type (wt) sGC coexpressed with DeltaPKG exhibited lower basal and NO-stimulated cGMP accumulation, whereas the S64A alpha1/beta1 sGC was resistant to the PKG-induced reduction in activity. Using purified sGC we observed that the S64D alpha1 phosphomimetic /beta1 dimer exhibited lower Vmax; moreover, the decrease in Km after NO stimulation was less pronounced in S64D alpha1/beta1 compared to wild-type sGC. Expression of a phosphorylation-deficient sGC showed enhanced responsiveness to endothelium-derived NO, reduced desensitization to acute NO exposure, and allowed for greater VASP phosphorylation. CONCLUSIONS: We conclude that PKG phosphorylates sGC on Ser64 of the alpha1 subunit and that phosphorylation inhibits sGC activity, establishing a negative feedback loop.

Inhibition of angiogenesis by the poly(ADP-ribose) polymerase inhibitor PJ-34.

Angiogenesis-related treatments have a broad spectrum of potential applications ranging from cancer to macular degeneration, to wound healing. Thus, the identification of pharmacological agents that modulate new blood vessel formation has attracted much attention. In the present study, we investigated the effects of the poly(ADP-ribose) polymerase (PARP) inhibitor PJ-34 [N-(6-Oxo-5,6-dihydro-phenanthridin-2-yl)-N,N-dimethylacetamide] on angiogenesis. Treatment of chicken chorioallantoic membranes (CAM) with PJ-34 reduced vascular length in these tissues; paradoxically, lower doses of PJ-34 (0.03 or 0.3 nmol/cm2) were more effective in inhibiting neovascularisation than higher doses (3 or 30 nmol/cm2). In vitro, incubation of endothelial cells (EC) with PJ-34 (300 nM to 10 microM) inhibited their proliferation in a concentration-dependent manner with maximal inhibition of 22.3% being observed at 10 microM. Capillary morphogenesis of EC grown on Matrigel was also negatively affected by PJ-34. In addition, PJ-34 abolished the migratory response to the prototype angiogenic factor vascular endothelial growth factor (VEGF) and reduced VEGF-stimulated activation of members of the mitogen activated protein kinase family (ERK1/2, p38), as well as Akt. PJ-34 also inhibited VEGF-induced NO release and cGMP accumulation. In conclusion, we provide evidence that PARP inhibition blocks angiogenesis-related EC properties by interfering with multiple signalling pathways leading to the inhibition of new blood vessel formation.

Design and synthesis of nitrate esters of aromatic heterocyclic compounds as pharmacological preconditioning agents.

Ischemic preconditioning (IPC) constitutes an endogenous protective mechanism in which one or more brief periods of myocardial ischemia and reperfusion render the myocardium resistant to a subsequent more-sustained ischemic insult. Pharmacological preconditioning represents an ideal alternative of IPC. We now describe the design and synthesis of indole, quinoline, and purine systems with an attached pharmacophoric nitrate ester group. The indole and quinoline derivatives 4 and 5 possess structural features of the nitrate containing K(ATP) channel openers. Purine analogues 11 and 12, substituted at the position 6 by a piperidine moiety and at position 9 by an alkyl nitrate, could combine the effects of the nitrate containing K(ATP) channel openers and those of adenosine. Compound 13 bears the nicotinamide moiety of nicorandil instead of nitrate ester. Compounds 4, 5, and 11 reduced infarction and the levels of malondialdehyde (MDA) at reperfusion in anesthetized rabbits. Compounds 12 and 13 did not significantly reduce the infarct size. Analogues 4 and 5 increased cGMP and MDA during ischemia, while combined analogue 4 and mitoK(ATP) blocker 5-hydroxydecanoic acid (5-HD) abrogated this benefit suggesting an action through mitoK(ATP) channel opening. Treatment with derivative 11 combined with 5-HD as well as treatment with 11 and adenosine receptor blocker 8-(p-sulfophenyl)theophylline (SPT) did not abrogate cardioprotection. Compound 11 is a lead molecule for the synthesis of novel analogues possessing a dual mode of action through cGMP-mitoK(ATP) channel opening-free radicals and through adenosine receptors.

cGMP-dependent and -independent angiogenesis-related properties of nitric oxide.

Nitric oxide exerts a stimulatory role during postnatal angiogenesis. Although soluble guanylyl cyclase (sGC) mediates many of the effects of nitric oxide (NO) in the vascular system, the contribution of cGMP-dependent vs cGMP-independent pathways in NO-induced angiogenesis remains unclear. Herein, we determined the effects of a NO donor (sodium nitroprusside; SNP) and a NO-independent sGC activator (BAY 41-2272) in the growth and migration of rat aortic endothelial cells (RAEC). RAEC lack enzymatically active sGC as suggested by their inability to accumulate cGMP upon exposure to SNP. However, treatment of RAEC with SNP promoted a modest increase in their proliferation and migration that was dependent on extracellular signal regulated kinase1/2 activation. Moreover, when RAEC were exposed to vascular endothelial growth factor we observed an increase in migration that was inhibited by NO synthase, but not sGC, inhibition. Infection of cells with adenoviruses containing sGC greatly increased the efficacy of SNP as a mitogenic and migratory stimulus. We conclude that NO is capable of stimulating EC proliferation and mobility in the absence of sGC; however, increased intracellular levels of cGMP following sGC activation greatly amplify the angiogenic potential of NO.

Effects of Levosimendan on circulating markers of oxidative and nitrosative stress in patients with advanced heart failure.

BACKGROUND: Oxidative stress is associated with maladaptive cardiac remodeling and vascular dysfunction and may be an important contributor to chronic heart failure (CHF) deterioration. We sought to investigate if the calcium sensitizer levosimendan beneficially modulates circulating markers of oxidative and nitrosative stress thus lessening their deleterious effects in patients with advanced CHF. METHODS: Thirty-nine patients with advanced CHF (mean NYHA 3.5+/-0.4; ischemic/dilated: 23/16; mean left ventricular ejection fraction: 26+/-7%) who were hospitalized due to syndrome worsening, were randomized (2:1) to receive either a 24-h levosimendan infusion of 0.1 microg/(kg min) (n=26) or placebo (n=13). Plasma b-type natriuretic peptide (BNP), circulating markers of oxidative [protein carbonyls, malondialdehyde (MDA)] and nitrosative (nitrotyrosine) stress, and cyclic GMP (cGMP) were measured at baseline and 48 h after each treatment. RESULTS: Baseline characteristics and medications were well balanced in the two treatment groups. A significant improvement in left ventricular ejection fraction (P<0.01), NYHA class (P<0.01), and plasma BNP (P<0.01) was observed post-treatment only in the levosimendan group. Markers such as MDA, protein carbonyls and nitrotyrosine remained stable in the levosimendan-treated group, but significantly increased (P<0.05) in the placebo-treated patients. Neither therapeutic intervention changed the levels of circulating cGMP. CONCLUSION: Levosimendan does not increase markers of oxidative and nitrosative stress in contrast to the placebo treatment, thus, exerting cardioprotective effects in advanced CHF patients. Moreover, levosimendan may exert its biologic action through non-cGMP-dependent biochemical pathways.

The phosphodiesterase 5 inhibitor sildenafil stimulates angiogenesis through a protein kinase G/MAPK pathway.

cGMP-degrading pathways have received little attention in the context of angiogenesis. In the present study we set out to determine whether cGMP-specific phosphodiesterase 5 (PDE5) inhibition affects new blood vessel growth. Incubation of chicken chorioallantoic membranes (CAMs) in vivo with sildenafil increased vascular length in a dose-dependent manner. Moreover, incubation of cultured endothelial cells (ECs) with the PDE5 inhibitor promoted proliferation, migration, and organization into tube-like structures. The effects of sildenafil on the angiogenesis-related properties of EC could be blocked by pre-treatment with the soluble guanylyl cyclase (sGC) inhibitor ODQ or the protein kinase G (PKG) I inhibitor DT-3. In addition, over-expression of sGC in EC led to an enhanced growth and migratory response to sildenafil. To study the signaling pathways implicated in the sildenafil-stimulated angiogenic responses we determined the phosphorylation status of mitogen-activated protein kinase (MAPK) members. Incubation of cells with sildenafil increased both extracellular signal regulated kinase 1/2 (ERK1/2) and p38 phosphorylation in a time-dependent manner. Inhibition of MEK by PD98059 and p38 with SB203580 blocked sildenafil-induced proliferation and migration, respectively, suggesting that these MAPK members are downstream of PDE5 and mediate the angiogenic effects of sildenafil. PDE5 inhibitors could, thus, be used in disease states where neo-vessel growth is desired.

Mastic oil from Pistacia lentiscus var. chia inhibits growth and survival of human K562 leukemia cells and attenuates angiogenesis.

Mastic oil from Pistacia lentiscus var. chia, a natural plant extract traditionally used as a food additive, has been extensively studied for its antimicrobial activity attributed to the combination of its bioactive components. One of them, perillyl alcohol (POH), displays tumor chemopreventive, chemotherapeutic, and antiangiogenic properties. We investigated whether mastic oil would also suppress tumor cell growth and angiogenesis. We observed that mastic oil concentration and time dependently exerted an antiproliferative and proapoptotic effect on K562 human leukemia cells and inhibited the release of vascular endothelial growth factor (VEGF) from K562 and B16 mouse melanoma cells. Moreover, mastic oil caused a concentration-dependent inhibition of endothelial cell (EC) proliferation without affecting cell survival and a significant decrease of microvessel formation both in vitro and in vivo. Investigation of underlying mechanism(s) demonstrated that mastic oil reduced 1) in K562 cells the activation of extracellular signal-regulated kinases 1/2 (Erk1/2) known to control leukemia cell proliferation, survival, and VEGF secretion and 2) in EC the activation of RhoA, an essential regulator of neovessel organization. Overall, our results underscore that mastic oil, through its multiple effects on malignant cells and ECs, may be a useful natural dietary supplement for cancer prevention.

Soluble guanylyl cyclase activation promotes angiogenesis.

Soluble guanylyl cyclase (sGC) is a cGMP-generating enzyme carrying a heme prosthetic group that functions as a nitric oxide (NO) sensor. sGC is present in most cells types, including the vascular endothelium, where its biological functions remain largely unexplored. Herein, we have investigated the role of sGC in angiogenesis and angiogenesis-related properties of endothelial cells (EC). Initially, we determined that sGC was present and enzymatically active in the chicken chorioallantoic membrane (CAM) during the days of maximal angiogenesis. In the CAM, inhibition of endogenous sGC inhibited neovascularization, whereas activation promoted neovessel formation. Using zebrafish as a model for vascular development, we did not detect any effect on vasculogenesis upon sGC blockade, but we did observe an abnormal angiogenic response involving the cranial and intersegmental vessels, as well as the posterior cardinal vein. In vitro, pharmacological activation of sGC or adenovirus-mediated sGC gene transfer promoted EC proliferation and migration, whereas sGC inhibition blocked tube-like network formation. In addition, sGC inhibition blocked the migratory response to vascular EC growth factor. Cells infected with sGC-expressing adenoviruses exhibited increased extracellular signal-regulated kinase 1/2 and p38 MAPK activation that was sensitive to sGC inhibition by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, suggesting that these mitogen-activated protein kinases are downstream effectors of sGC in EC. A functional role for p38 in cGMP-stimulated migration was demonstrated using SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole]; pharmacological inhibition of p38 attenuated BAY 41-2272 [5-cyclopropyl-2-[1-(2-fluoro-benzyl)-1H-pyrazolo[3,4-b]pyridin-3-yl]-pyrimidin-4-ylamine] and sGC overexpression-induced EC mobilization. We conclude that sGC activation promotes the expression of angiogenesis-related properties by EC and that sGC might represent a novel target to modulate neovessel formation.

Soluble guanylyl cyclase: more secrets revealed.

Guanylyl cyclases (GCs) are enzymes that convert guanosine-5'-triphosphate (GTP) to cyclic guanosine-3',5'-monophosphate (cGMP). The second messenger cGMP participates in signaling by (1) stimulating the activity of kinases that belong to the protein kinase G family, (2) altering the conductance of cGMP-gated ion channels and (3) changing the activity of cGMP-regulated phosphodiesterases. In contrast to adenylyl cyclases which exist as membrane-bound molecules, guanylyl cyclases (GC) occur in both membrane-bound and cytosolic forms. The particulate GC (pGC) isoforms serve as receptors for natriuretic peptides, while soluble GC (sGC) is the "receptor" for nitric oxide (NO). In addition to the difference in ligands and subcellular organization, the two forms of GC also differ in that pGC exists in homodimeric form, while typically sGC occurs as a heterodimer. Herein, we will review the literature on sGC subunit structure and discuss the regulation of the enzyme at the transcriptional and post-translational level.